The higher density and higher S/N ratio of recent magnetic recording medium such as a magnetic tape requires increasingly finer-sized magnetic powder.
According to a widely accepted theory, the S/N ratio of a magnetic recording medium is proportional to the square root of a number of magnetic particles in a specific amount of recording material that is responsible for recording and reproducing data. Therefore, if a specific weight of magnetic powder is employed for coating, a powder of smaller particle size is more advantageous in improving the S/N ratio. Additionally, using finer magnetic particles for improving the BET value of the magnetic powder accordingly results in smooth-surfaced magnetic layer, and, also, smaller spacing loss, this in turn is advantageous in attaining higher electromagnetic conversion properties. Using magnetic metal powder enables further enhanced high-density recording, thereby improves the performance of the magnetic recording medium.
To sum up, the magnetic metal powder has large saturated magnetization and large coersive force, and therefore, excels in characteristics for high-density recording material. However, its high surface activity incurs the following two problems:
(1) Oxidation resistance of magnetic metal powder in air The magnetic metal powder, when allowed to stand in air, gradually develops deterioration in magnetic property due to progressive oxidation. PA1 (2) Dispersibility in binder
Higher surface activity of magnetic metal powder, when the powder is dispersed in a binder, results in poor dispersibility of the powder. Dispersing the magnetic metal powder is quite difficult, and, in the worst case, the similar powder gelate a binder resin in a coating solution.
The scope of applications of video tapes has been more diversified recently, and video tapes are subjected to various operating conditions. Therefore, good corrosion resistance is required of video tapes.